Optimize sorting an Array from another Array

Question

I have two arrays, one containings some items, and another containings sorted ids of those items like so:

const items = [
    { id: 1, label: 'foo' },
    { id: 2, label: 'bar' },
    { id: 3, label: 'lorem' },
    { id: 4, label: 'ipsum' },
]

const sortedItemIds = [4, 3, 2, 1]

I want to have another array containing items sorted by their id like so:

const sortedItems = [
    { id: 4, label: 'ipsum' },
    { id: 3, label: 'lorem' },
    { id: 2, label: 'bar' },
    { id: 1, label: 'foo' },
]

Note that the order may not be whatever, not asc or desc

I made this piece of code, that works pretty well as it:

let sortedItems = []
sortedItemIds.map((itemId, index) => {
    items.map(item) => {
        if (item.id === itemId) {
            sortedItems[index] = item
        }
    }
})

I feel like I may run into issues with a large array of items, due to the nested Array.map() functions

Is there a better way / best practice for this scenario?

None of the .map() calls return anything, hence they are not the right tool for the task — Andreas
– Andreas, Commented Oct 1, 2018 at 16:59
Possible duplicate of Javascript - sort array based on another array — Andreas
– Andreas, Commented Oct 1, 2018 at 17:00

Nenad Vracar · Accepted Answer · 2018-10-01 17:03:46Z

3

You could create one object where keys are ids and then use that object get values by id.

const items = [{ id: 1, label: 'foo' },{ id: 2, label: 'bar' },{ id: 3, label: 'lorem' },{ id: 4, label: 'ipsum' }]
const sortedItemIds = [4, 3, 2, 1]

const obj = {}
items.forEach(o => obj[o.id] = o);

const sortedItems = sortedItemIds.map(e => Object.assign({}, obj[e]));
console.log(sortedItems)

answered Oct 1, 2018 at 17:03

Nenad Vracar

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3 Comments

Patrick Roberts Over a year ago

The Object.assign({}, ...) seems unnecessary here. OP has not mentioned any requirement about performing a shallow clone of each of the objects and in any case the use of Object.assign() should at least have a brief explanation.

pistou Over a year ago

What if the item's id is not an Int, but let's say a String? And in case of mixed types?

pistou Over a year ago

Nevermind I didn't understand your code. Seems pretty good to me now!

Ele · Accepted Answer · 2018-10-01 17:01:09Z

1

You don't need the function map for doing this, just use the find Array.indexOf and Array.sort in order to sort it.

const items = [{ id: 1, label: 'foo' },{ id: 2, label: 'bar' },{ id: 3, label: 'lorem' },{ id: 4, label: 'ipsum' }],
      sortedItemIds = [4, 3, 2, 1];

items.sort((a, b) => sortedItemIds.indexOf(a.id) - sortedItemIds.indexOf(b.id));
console.log(items);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 1, 2018 at 17:01

Ele

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2 Comments

pistou Over a year ago

Looks like this solution works well. I modified it for my needs, adding .slice() as I didn't want to change my first array. const sortedItems = items.slice().sort((a, b) => sortedItemIds.indexOf(a.id) - sortedItemIds.indexOf(b.id));.

Patrick Roberts Over a year ago

The efficiency of this is O(n^2 log n), whereas @NenadVracar's answer is ~O(n) assuming approximately constant time for key lookup. Not exactly an optimized implementation.

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